Stretched fluoropolymers

ABSTRACT

The present invention is directed to stretched filaments based on fluoropolymers, where the filaments were stretched at a temperature between 70° C. and the Vicat temperature and where the filaments are cooled under full tensile load to room temperature.

The present invention is directed to stretched filaments based on non-perfluorinated fluoropolymers, where the filaments were stretched at a temperature between 70° C. and the Vicat temperature and where the filaments are cooled under full tensile load to room temperature.

Fibre-reinforced materials are usually based on the use of glass fibres or carbon fibres in polymers. This raises the fundamental problem of compatibility of the fibres with the matrix material and resultant problems in achieving binding between reinforcing material and matrix. This is often a particular problem when thermoplastics are used as matrix. These materials are moreover not recyclable, because it is very difficult to remove the fibres.

The main disclosures in the prior art relate to two processes for the stretching of polyolefins, for example polyethylene or polypropylene: the melt spinning process (WO 2004/028803 A1) and the gel spinning process (WO 2010/057982 A1). Polyolefins can easily be stretched at room temperature; the stretching speed selected here must be relatively low because of the exothermicity of stretching. The stretched polyolefins have the disadvantage that they exhibit very high shrinkage after stretching when processed at elevated temperatures and therefore first have to be equilibrated at the desired operating temperature. Stretched polyolefins moreover have very restricted mechanical properties which limit their usefulness as reinforcing fibres. Particular disadvantages are lack of thermal stability and lack of compressive strength (cold formability).

Omar (Master's degree thesis: “Processing, morphology and product parameters of PVDF filaments for biomedical applications”, August 2008, Institut für Textiltechnik RWTH Aachen, Prof. Dr. Thomas Gries) discloses stretching procedures applied to PVDF fibres for the production of yarns and textiles; these were stretched by a factor of at most 2.5.

DE 60024882 T2 discloses a two-stage stretching process for PVDF fibres for the production of fishing lines. In order to achieve ideal mechanical properties, the fibres are subjected to controlled shrinkage at a temperature of at least 220° C. for a few seconds.

WO 2013/190149 A1 discloses ductile fibres of various thermoplastics, preferably polypropylene and polyethylene, as a constituent of what are known as prepregs. These are understood to be weaves of thermoplastic fibres with brittle fibres, in particular carbon fibres. These materials are then preferably pressed or thermoformed in a matrix made of the material of the ductile fibres. This melts the ductile fibre and improves binding between matrix and brittle fibre.

Production of entirely aromatic polyamide fibres, for example poly(p-phenylene terephthalamide) (PPTA, aramid) with trademarks: Kevlar® (trademark of DuPont, USA), Twaron® (trademark of Teijin Lim, Japan) is described in U.S. Pat. No. 3,869,430 A.

EP 0091766 A2 and DE 2304429 A1 describe stretching procedures for perfluoropolymers. Stretching factors obtained in these cases are at most 4.5; attempts to achieve greater stretching lead to fibre breakage. It also appears that the stretching procedure only improves the mechanical properties of perfluorinated polymers to a very limited extent: modulus of elasticity after stretching is at most 1228 MPa.

For the purposes of this invention, the term “filament” means fibres, films or ribbons.

Films in particular are preferably stretched in more than one direction.

The term “stretching” means a tensile procedure which is carried out after extrusion has been concluded through use of thermal and mechanical energy.

It was therefore an object of the present invention to produce stretched filaments made of fluoropolymers, and to provide a simple, non-hazardous and solvent-free process for the stretching of fluoropolymers.

The object was achieved via stretched filaments made of non-perfluorinated fluoropolymers, where the filaments are cooled after stretching under full tensile load.

The present invention provides a process for the production of stretched filaments comprising at least 80% by weight, preferably 85% by weight, more preferably 90% by weight, still more preferably 95% by weight, of fluoropolymers, and in particular consisting thereof, characterized in that

the filaments have a rectangular cross section where the thickness is less than the width, where the raw filaments are stretched with a stretching factor (SF) greater than or equal to 3 at a stretching temperature between 70° C. and the Vicat temperature, which is determined in accordance with DIN EN ISO 306:2004-10 B50, where the filaments are cooled under full tensile load to below 50° C., where no perfluorinated polymers are present.

The invention further provides stretched filaments produced by the process of the invention.

The invention further provides the use of the stretched filaments of the invention for the production of composites.

The invention further provides the use of the stretched filaments of the invention for the production of winding layers.

An advantage of the stretched filaments of the invention is that they exhibit little shrinkage at elevated temperature, i.e. exhibit almost no relaxation effect.

It is also advantageous that the stretched filaments of the invention have high mechanical stability. Mechanical stability is preferably measured as breaking stress in the direction of stretching.

It is also advantageous that the stretched filaments of the invention have surprising elasticity at relatively high stretching factors.

It is also advantageous that the stretched filaments of the invention have high mechanical stability, and that this is also true at elevated temperature.

The stretched filaments of the invention, the composites of the invention comprising the filaments of the invention, and the production and use according to the invention are described by way of example hereinafter, without any intention that the invention be restricted to these illustrative embodiments. Where ranges, general formulae, or classes of compound are stated below, these are intended to comprise not only the corresponding ranges or groups of compounds explicitly mentioned, but also all subranges and subgroups of compounds that can be obtained by extracting individual values (ranges) or compounds. Where documents are cited for the purposes of the present description, their entire content is intended to be part of the disclosure content of the present invention. Where percentage data are provided hereinafter, these are data in % by weight unless otherwise stated. Percentage data for compositions are based on the entire composition unless otherwise stated. Where average values are provided hereinafter, these are averages by mass (averages by weight) unless otherwise stated. Where measured values are provided hereinafter, unless otherwise stated these measured values were determined at a pressure of 101 325 Pa and at a temperature of 25° C.

The scope of protection includes finished and packaged forms that are conventionally used in commerce for the products of the invention, not only per se but also in possible comminuted forms to the extent that these are not defined in the claims.

Fluoropolymers can be selected from polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-perfluoroalkylvinyl ether-tetrafluoroethylene copolymer (CPT), tetrafluoroethylene-hexafluoropropene copolymer (FEP) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ETFE modified by a tercomponent, for example propene, hexafluoropropene, vinyl fluoride or vinylidene fluoride (for example EFEP); moreover also copolymers based on vinylidene fluoride which comprise up to 40% by weight of other monomers, for example trifluoroethylene, chlorotrifluoroethylene, ethylene, propene and hexafluoropropene.

Fluoropolymers of the filaments of the invention are not perfluorinated polymers. The fluoropolymers preferably have hydrogen alongside fluorine as substituents on carbon; more preferably, the carbon atoms of the backbone, i.e. the carbon atoms that form the polymer chain, exhibit some extent of hydrogen substitution. It is still more preferable that there is hydrogen substitution on at least 5 mol % of the carbon atoms of the fluoropolymers, preferably at least 10 mol %, 20 mol %, 30 mol % or 40 mol %, and in particular 50 mol %; the corresponding upper limits are preferably 90 mol %, 80 mol %, 70 mol %, 60 mol % and in particular 50 mol %. These content data are particularly preferably based on the carbon atoms of the backbone of the fluoropolymers.

It is preferable that the fluoropolymers of the filaments of the invention exhibit branching only at no more than 25% of the carbon atoms of the backbone; branching occurs where there are carbon-carbon bonds between a backbone carbon atom and another carbon atom. More preferably, the fluoropolymers have branching at no more than 20%, 15%, 10%, or 5% of carbon atoms of the backbone, and with particular preference at no carbon atom of the backbone.

It is further preferable that the fluoropolymers of the filaments of the invention have no ether groups.

Fluoropolymers of the filaments of the invention are preferably selected from polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), polychlorotrifluoroethylene (PCTFE), ETFE modified by a tercomponent, for example propene, or modified by vinylidene fluoride; moreover also copolymers based on vinylidene fluoride which comprise up to 40% by weight of other monomers. PVDF is in particular preferred.

It is preferable that the fluoropolymers comprise no solvents.

The Vicat temperature of the fluoropolymers of the filaments of the invention is preferably at least 80° C., more preferably at least 90° C., still more preferably at least 110° C., particularly preferably at least 125° C. and with particular preference at least 140° C.

The Vicat temperature is known to the person skilled in the art and is preferably determined in accordance with DIN EN ISO 306:2004-10, B50. The required temperature in each case has a tolerance of plus/minus 5° C.; for the value 140° C., therefore, the values 135° C. to 145° C. are included.

The width to thickness ratio of the filaments of the invention is preferably at least 25 to 1, more preferably at least 50 to 1, still more preferably at least 100 to 1, particularly preferably at least 200 to 1, more particularly preferably at least 300 to 1, with particular preference at least 400 to 1.

Preference is given to a stretching temperature of from 70° C. up to the Vicat temperature [° C.], more preferably 85° C. to 5% below Vicat temperature [° C.] and with particular preference 100° C. to 10% below Vicat temperature [° C.].

The filaments of the invention have been produced by stretching of the raw filaments by a stretching factor (SF) that is preferably greater than or equal to 3, more preferably greater than or equal to 5, with particular preference greater than or equal to 10, or greater.

The person skilled in the art is familiar with determination of the stretching factor. It is preferably determined by determining the length of the raw filament before stretching and of the filaments after stretching. The factor is then calculated by dividing the lengths after stretching by the lengths before stretching. The stretching factor is stated as numerical value of 1 or greater, or else as corresponding percentage value in which the numerical value of 1 then corresponds to 100%.

It is preferable that, starting from a stretching factor of 3.0, the filaments of the invention have high elasticity; the elasticity is preferably expressed as modulus of elasticity.

It is more preferable that, with a stretching factor of 3.0, the modulus of elasticity of the filaments of the invention has risen to less than twice the value for the unstretched input material, preferably less than 1.5 times the said value.

The rise of the modulus of elasticity starting from a stretching factor (SF) of 3.0 is still more preferably only up to 150 MPa for each stretching-factor change of 1.0, particularly preferably up to 120 MPa, with particular preference up to 100 MPa.

In particular, for a rise of the stretching factor from 3 to 4 the modulus of elasticity rises by at most 150 MPa, by at most 120 MPa and very particularly by at most 100 MPa.

It is preferable that the filaments of the invention have been stretched in free space, without contact. The zone in which the stretching takes place is a zone in which the ambient atmosphere is heated, therefore by way of example being a type of tube oven or the space between at least two heated plates.

The filaments of the invention can be stretched continuously or batchwise.

Preference is given to static stretching procedures, i.e. stretching procedures in which one end of the filament remains stationary with speeds of 10 mm/min up to 200 mm/min, preferably of 20 mm/min up to 100 mm/min, more preferably 30 mm/min to 80 mm/min.

Preferred continuous stretching procedures are carried out in a manner that provides a low transport speed preferably in the range from 10 mm/min up to 3000 mm/min, preferably from 50 mm/min up to 2500 mm/min, more preferably 100 mm/min to 2000 mm/min, even more preferably 500 mm/min to 1500 mm/min. The speed of the faster-running transport unit is calculated by way of the stretching factors.

The filaments of the invention can be stretched by a single stretching procedure or by a number of successive stretching procedures. The latter case always requires selection of a relatively high stretching temperature. A single stretching procedure is more preferable.

The filaments of the invention are cooled after the stretching procedure to below 50° C. This cooling preferably takes place slowly, preferably for at least 10 seconds, more preferably for at least 20 seconds, still more preferably for at least 30 seconds, particularly preferably for at least 45 seconds, with particular preference for at least 1 minute.

The stretched filaments of the invention preferably exhibit only minor shrinkage/relaxation in the direction of tension when heated to a temperature (relaxation temperature) below the melting point.

It is preferable that the relaxation temperature is above 25° C. and below the melting point, preferably below the stretching temperature.

Relaxation of the filaments of the invention is preferably at most 6%, based on the stretched length, preferably at most 5.5%, more preferably at most 5%, still more preferably at most 4.5%, and with particular preference at most 4%.

It is preferable that the relaxation of the filaments of the invention does not take place under tensile stress.

It is preferable that the length of the stretched filaments of the invention is greater than 5 times a dimension situated at right angles to the length; it is preferable that the filaments are what is known as continuous filaments. The length of the filaments is always determined in the direction of tension.

For the purposes of this invention, the term “filament” means fibres, films or ribbons.

Films in particular are preferably stretched in more than one direction.

It is preferable that the filaments do not have a round cross section.

The individual filaments can be used to manufacture composites; preferred composites of ribbons are therefore laid scrims, weaves such as mats, and also mixed forms.

Laid scrims can consist either of filaments cut-to-size to a particular length or of continuous filaments in the form of windings around, for example, tubes.

Preferred laid scrims made of continuous filaments of the invention are winding layers around hollow bodies, the filaments here preferably being ribbons. Winding is preferably unidirectional or multidirectional. Multidirectional winding layers exhibit an angle in relation to the direction of tension of the filaments. This angle is preferably in the range from 5° to 120°, more preferably from 30° to 90°, with particular preference 15° to 80°. In the case of winding layers around tubes, these winding layers exhibit an angle of inclination in relation to the centre of the tube. It is preferable that different winding layers exhibit different angles of inclination. The design of the winding layers around tubes in relation to the angle of inclination is preferably such that after one rotation the edges of the layer are flush with, and adjoin, one another.

It is preferable that no yarns are produced from the filaments, where yarns are preferably produced from a plurality of individual filaments by braiding (e.g. plaits and cords) or by twisting (e.g. cables); in particular, no yarns are produced from filaments with round cross section.

EXAMPLES

Materials:

PVDF: Solef® 1006, trademark of Solvay, USA

PVDF: Solef® 6008, trademark of Solvay, USA

FEP: Neoflon® NP-20, trademark of Daikin Industries, Japan

Methods

DSC:

Perkin Elmer Diamond, automatic peak recognition and integration by a method based on DIN EN

ISO 11357-1: 2010, heating rate 20 K/min.

Vicat:

DIN EN ISO 306:2004-10, Method B, 50 N (loading 5 kg).

Example 1a, Production of Specimens

An extruder (Collin E45M) was used at a temperature of 260° C. to extrude PVDF (Solef 1006), which was calendered to give a ribbon of thickness 650 μm and width 35 mm and cooled to 57° C. Take-off speed was 1.4 m/min.

E 1,* are samples made of PVDF Solef 1006;

E 2,* are samples made of FEP.

Example 1 b, Production of Specimens

An extruder (Collin CE20) was used at a temperature of 240° C. to extrude PVDF (Solef 6008), which was calendered to give a ribbon of thickness 150 μm and width 120 mm and cooled to 89° C.; take-off speed was 2.1 m/min.

E 3,* are samples of this Example 1 b.

Example 2, Stretching of Specimens

Method 1:

Specimens according to Example 1a were stretched in a tensile tester (Zwick, Z101-K) at 10 mm/min at 140° C. Before the tensile load was released, the specimens were cooled to below 50° C.

Method 2:

An endless specimen according to Example 1a was provided on a reel and stretched on a continuously operating machine (Retech drawing machine) at a material-feed rate of 4 rpm with a tension rate of up to 32 rpm to give a stretching factor (SF) of 8. The stretching temperature was 140° C.

Method 3:

Specimens according to Example 1a were stretched in a tensile tester (Zwick, Z101-K) at 10 mm/min at 100, 120 and 140° C. Before the tensile load was released, the specimens were cooled to below 50° C. The stretched specimens thus produced were again clamped into the machine and were again stretched at 100, 120 and 140° C. at 10 mm/min.

Table 2 presents the results.

Method 4:

An endless specimen according to Example 1 b was provided on a reel and stretched on a continuously operating machine (Retech drawing machine) at a material-feed rate of 1.5 m/min and at variable tension rates to realize various stretching factors (SF). The stretching temperatures were 120° C.

Table 3 presents the results.

Method 5:

An endless specimen according to Method 4 (stretched with SF=6) was provided on a reel and stretched on a continuously operating machine (Retech drawing machine) at a material-feed rate of 1.5 m/min and at variable tension rates to realize various stretching factors (SF). The stretching temperatures were 120° C.

Table 4 presents the results.

Example 3a, Mechanical Tests

Tensile Tests

Dumbbell specimens in accordance with DIN 527-2:2012 (specimen type 1BA) were punched out of the stretched (Method 1) ribbons; the thickness resulted from the stretching test and was not altered.

Test equipment from Zwick was used to test tensile strength at a temperature of 23° C. and relative humidity of 50%. Test speed=10 mm/min, clamped length=120 mm and measurement length of incremental gauge=75 mm.

The results are provided in Table 1, and also in FIGS. 1 and 2.

The results are the arithmetic average from 3 specimens.

Example 3b, Mechanical Tests

Tensile Tests

Tensile strength in accordance with DIN 527-2:2012 was measured from the stretched (Methods 4 and 5) ribbons; the thickness resulted from the stretching test and was not altered.

Test equipment from Zwick was used to test tensile strength at a temperature of 23° C. and relative humidity of 50%. Test speed=60 mm/min, clamped length=100 mm.

The results are provided in Table 4, and also in FIGS. 3 and 4.

The results are the arithmetic average from 3 specimens.

TABLE 1 T = 23° C., results of the tensile tests according to Example 3a. E 1.0 E 1.1 E 1.2 E 1.3 Stretching factor 1 1.4 3.0 4.5 Modulus of elasticity [MPa] 2144 2965 3367 3323 Max strength (stress) σ_(m) [MPa] 58.02 173.34 248.60 284.64

TABLE 2 Results of the stretching tests according to Example 2, Method 3. Stretching temperature [° C.] Stretching procedure 100 120 140 Stretching factor during 1st 5.00 5.34 5.12 stretching procedure Stretching factor during 2.03 2.17 2.45 2nd stretching procedure Overall stretching factor 10.15  11.59  12.54 

TABLE 3 Results of the stretching tests according to Example 2, Method 4. Speed of stretching reel Stretching Speed of 1st reel [m/min] [m/min] factor 1.5  9.0 6.0 1.5 10.6 7.1 1.5 12.0 8.0 1.5 13.6 9.0 1.5 15.2 10.1 

TABLE 5 Results of the stretching tests according to Example 2, Method 5. Stretching procedure E 3.1 E 3.2 E 3.3 Stretching factor during 1st 6 6 6 stretching procedure Stretching factor during 1.21 1.32 2.15 2nd stretching procedure Overall stretching factor 7.30 7.96 8.63

TABLE 4 Results of the tensile tests according to Example 3b. E 3.4 E 3.5 E 3.6 E 3.7 Stretching factor 1 6 7.3 8.6 Modulus of elasticity [MPa] 1200 2160 2390 2670 Max strength (stress) σ_(m) [MPa] 49.6 301 350 370 

1. A process for producing stretched filaments comprising at least 80% by weight of at least one fluoropolymer, the process comprising: stretching raw filaments with a stretching factor greater than or equal to 3 at a temperature between 70° C. and a Vicat temperature of the at least one fluoropolymer, which is determined in accordance with DIN EN ISO 306:2004-10 B50, and cooling the raw filaments after stretching under full tensile load to below 50° C., wherein the stretched filaments have a rectangular cross section where a thickness thereof is less than a width thereof, wherein the stretched filaments are made of non-perfluorinated polymers.
 2. The process according to claim 1, where the at least one fluoropolymer is selected from the group consisting of polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), polychlorotrifluoroethylene (PCTFE), ETFE modified by a tercomponent or modified by vinylidene fluoride, and copolymers based on vinylidene fluoride which comprise up to 40% by weight of other monomers.
 3. The process according to claim 1, where the Vicat temperature of the at least one fluoropolymer is at least 80° C.
 4. Stretched filaments produced by the process according to claim 1, having a width to thickness ratio of at least
 25. 5. A composite comprising the stretched filaments according to claim
 4. 6. A winding layer comprising the stretched filaments according to claim
 4. 